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Air in Fuel System, How to bleed???

Qwert98

Jr. Member
Joined
Feb 15, 2013
Messages
72
Hi, I have a 1973 EB with a 302. The mechanical fuel pump and gas tank is a couple years old. I just had the tranny rebuilt, and it sat for a couple months. I picked it up and it rand great for 5 miles or so, until I ran out of gas. The gas station was 1/4 mile, so I cranked her up, hoping to make it there. I only got another 50 yards before she was stopped again. Cranking did not help anymore.
I added fuel and it ran well for a mile or so. I cranked for a while and nothing. I sprayed starting fluid and it fired right up and ran another mile or so. Same thing happened for the next 2-3 miles home, until I could only get 1/4 mile per start.
Fuel filter was clean when I inspected it. I unhooked the end that screws into the carb, and put it in a bottle and cranked a few times, and it appeared to have a good flow (only ran 2-3 oz). Tried driving it again and same issue.
I'm open to suggestions, but I assume I have air in my fuel system. Any advice how to bleed? I was going to run the fuel line into a gas tank and cycle a gallon or so through, but i'd love to hear an alternate suggestion on the root cause, or a good bleeding method...

Thanks!!

Adam
 

Rustytruck

Bronco Guru
Joined
Feb 24, 2002
Messages
10,875
A stock fuel system only has pressure after the pump going to the carb any leak there is self evident. From the pump to the gas tank/tanks the fuel system is under suction. leaks there let air in and not fuel out unless severely compromised. so you need to start at the tank and make sure the fuel line is in good shape and all connections are tight and not leaking air in. if you have 2 or more tanks check the selector valve under the drivers seat. Its easy for air to leak in the old selector valve as there is a single O-ring in there to make seal at the valve shaft. The cap of the valve comes off so the seal can be replaced. Unfortunately you have to remove the valve to get a wrench on it for O-ring replacement. Make sure plugged venting on the fuel system isn't creating this problem for you.
 
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Qwert98

Jr. Member
Joined
Feb 15, 2013
Messages
72
Thanks for the quick reply.
It only has one fuel tank, and I inspected the line and nothing obvious. I could pressurize fuel tank (with air line) to see if anything is leaking if you think its' worthwhile. It seems like the fact that this started right after I ran out of fuel, should be important?
If fuel line is pumping, is there no reason to bleed? Any other suggestions?
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,344
And you should try to drive it with the gas cap removed to make sure it's not blocking the inflow of air into the tank.
Your '73 would have had the full complement of venting, including the EVAP system with charcoal canister at the passenger front wheel well on the frame, and condensing tank behind the driver's shoulder. Is that all still intact?

When it's starving, have you looked down the carb with the filter off and moved the throttle lever to see if you have two nice streams of gas coming out of the squirters?

The fact that you got flow through the filter during your check means that it's flowing fuel, both from the pump and through the filter. But maybe the pump is weak and is not flowing through into the float bowl?
How old is the pump? And even more important sometimes, how often does it sit unused, and for how long?
Don't see where you live, but if your fuel is big in the ethanol department, you may just have a ready-to-retire fuel pump.

But for sure check the lines as well. Just can't ignore any other aspects yet.

Good luck.

Paul
 
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Qwert98

Jr. Member
Joined
Feb 15, 2013
Messages
72
Thanks Paul. the fuel pump is about 2 years old.

Regarding "Your '73 would have had the full complement of venting, including the EVAP system with charcoal canister at the passenger front wheel well on the frame, and condensing tank behind the driver's shoulder. Is that all still intact?"

No, that is all gone. Fuel line goes straight into the pump, but I've had the Bronco 6 years it's never been an issue. I can try driving with gas cap off, but the cap gasket is mostly gone, so I would not think it would create a vacuum.

It did sit about 6 weeks before I ran it dry, but the non-ethanol fuel was new. That's all I use BTW. I live in SC...

I'll look down the carb and actuate throttle next time it stalls out to look for fuel. Would I need to crank while I do that? Good idea...
 
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DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,344
...the fuel pump is about 2 years old.
It did sit about 6 weeks before I ran it dry, but the non-ethanol fuel was new. That's all I use BTW. I live in SC...

I don't want to sound like a Chicken Little/The sky is falling type of member yet, but my first thought when I read those comments was "ooh, that's a bad thing!" right off the bat.
The reason is that newer parts are not as good as old, and newer parts hate to sit for extended periods, and new pumps hate to be run dry under certain circumstances.
I could run my old original pump dry on every tank (which I did in fact) and it would last for 85k miles before sucking wind on the Rubicon one day.
But I've seen newer pumps fail after the first time it was run dry.

I've also seen pumps that were new (this is about 10 years ago now) that were only run for a few minutes at a time for a total of maybe an hour, then sat for six months and the next time the engine was fired fuel just dripped out of every pore of the almost-new pump.

So at this point, I think a pump test is called for at least.

Regarding "Your '73 would have had the full complement of venting, including the EVAP system with charcoal canister at the passenger front wheel well on the frame, and condensing tank behind the driver's shoulder. Is that all still intact?"

No, that is all gone. Fuel line goes straight into the pump, but I've had the Bronco 6 years it's never been an issue. I can try driving with gas cap off, but the cap gasket is mostly gone, so I would not think it would create a vacuum.

If it was not an issue before, you're right that it should not be now. But it wouldn't hurt (because it's free!) to pull the cap anyway. With the bad gasket you're probably right, but might as well know for sure.

I'll look down the carb and actuate throttle next time it stalls out to look for fuel. Would I need to crank while I do that? Good idea...

Nope. Just peek down inside and watch without the engine running. No need for it to be running at this point. You're just making sure there is gas getting to the carburetor. While it sounds like a pump/delivery issue, you need to rule out anything else.
If there is plenty of gas getting to the carb and it still won't run consistently, you may be dealing with either with multiple issues, or another issue entirely.

Paul
 
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Qwert98

Jr. Member
Joined
Feb 15, 2013
Messages
72
I ran about a gallon through the fuel pump into a gas can, so I do not believe there is air in the line anymore. I removed the gas cap and drove a Mile or so and it stalled out again. I looked down the carburetor barrel and no fuel was squirting into it while it was in the stalled out condition. I looked down there before I started driving then again after I got it running and shut it off and I did see the fuel squirt that you were referencing. Does this mean the fuel pump is shot? Could the float be sticking in the carburetor? When I cranked the engine with the fuel line in a separate gas tank, the flow was is not as significant as it was yesterday
Thanks in advance for all of your time and diagnostic help!!
 

metal1

Full Member
Joined
May 2, 2016
Messages
259
Loc.
hidesert ,socal
sounds to me it needs a fuel pump. a good pump will have 3-4 psi and flow a bunch of fuel,,,and on the "its a new part " get this guys NEW puppys die also ..sorry to be harsh but a pump is cheep and only takes a few mins to swap out
 

bronkenn

Contributor
Bronco Guy
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Apr 27, 2017
Messages
2,662
Loc.
Southeast Ohio
Might want to check the pick up in the tank. Sounds like when it sits for a minute or so it will run for a bit then stall out. I have seen where debris in the tank will clog the pick up when it runs and then when it stalls the debris will fall away from the pick up allowing it to start again until it picks up the debris again and stalls. A soft rubber suction hose can do the same thing. Good luck, Ken
 

LilMixedUp

Full Member
Joined
Feb 27, 2016
Messages
161
Loc.
Bonaire
second brokenn... I had that issue a few years back, pick-up was in fact picking up trash and clogging the line. Ended up pulling tank cleaning and changing all the internal lines. Been running like a top ever since. Good Luck
 
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Qwert98

Jr. Member
Joined
Feb 15, 2013
Messages
72
Yes, the fuel line is within a couple inches above the exhaust. But keep in mind that it has been like that since I have owned the bronco and this issue has only started since I ran the tank dry.
 
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Qwert98

Jr. Member
Joined
Feb 15, 2013
Messages
72
Thanks for all the advice, I have a few things to try now. Since I dropped the tank (newer clean tank) a couple years ago, I’ll replace the fuel pump first. I’ll let everyone know what I find. Fuel pump is a pretty cheap/easy replacement. And this time I won’t just go with the cheapest one I can find ;)
 

charlie6976

Sr. Member
Joined
Jan 19, 2014
Messages
404
Loc.
Grand Coulee WA
Before replacing the fuel pump, try this. Connect a spare piece of fuel line to the inlet side of your fuel pump. Put the other end in your lawn mower (or similar) gas can. Now start your engine. If it sucks gas and runs, I would say look at your rubber line hose/hose connections. Probable old, cracked and rotted. Well mine were and sucked air.
You can use compressed air into the tank to find leaks, but first disconnect the line from the fuel pump so you don't ruin the diaphragm in the pump.
 
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Qwert98

Jr. Member
Joined
Feb 15, 2013
Messages
72
I replace the fuel pump, had the same issue in about 2 miles. It does not seem to happen when idling or putting around the neighborhood at low speed, so I cannot try that trick of putting the intake to the fuel pump into a gas can. I could try compressing the fuel tank to look for line leaks, but that would be coincidental that the leak formed at the same time that I ran out of gas.
I wonder if the float could be sticking in the carb? Again that would be coincidental to have started right when I ran out of gas.
I wonder if it could be sucking up something out of the fuel tank, but the tank was completely empty out and new as of a couple years ago. It is also worth noting that if I dump a little gas into the barrel it starts right up and drives again.

This one has me baffled...

Adam
 
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Qwert98

Jr. Member
Joined
Feb 15, 2013
Messages
72
I could hook up a small gas tank to the inlet to the fuel pump and secure it under the hood to drive around and perform the test. I suppose that could rule out sucking up stuff from the fuel tank.
 

charlie6976

Sr. Member
Joined
Jan 19, 2014
Messages
404
Loc.
Grand Coulee WA
You could put in a temporary rubber line from the tank to the fuel pump. That would narrow things down (maybe). I would try this. It's simple, just zip tie the line up out of the way. I think your fuel system is sucking air somewhere.
 
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Qwert98

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Feb 15, 2013
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